The exemplary embodiments are directed to directional control seat valves.
In DE utility model G 91 09 976 a 4/2-way directional control seat valve is disclosed which is formed by two 2/2-way directional control seat valves each adapted to be actuated by means of a magnet. Each 2/2-way directional control seat valve comprises a valve cone which is biased against a valve seat by a spring. By means of the valve cone it is possible to open the connection between an inlet port and an outlet port. The known seat valve is executed so as to be pressure-balanced relative to one of the ports. To this end a compensating piston is formed on a piston carrying the valve cone, the rear-side end face removed from the valve seat of which is subjected to the pressure at one of the ports via a compensating passage, so that the piston is pressure-balanced relative to this port. In the known solution the compensating piston is executed integrally with the piston carrying the valve cone. In order to be able to introduce this piston into a valve bore, the diameter of the compensating piston must be selected somewhat smaller than the valve seat diameter. Moreover a play is required in order to ensure mobility of the compensating piston in the valve bore. Owing to the differential area between the diameter of the compensating piston and the valve seat diameter, the piston is acted on in the closing direction or in the opening direction in accordance with the one port at which the high pressure is present, so that correspondingly the spring acting on the valve cone in the closing direction must be designed to be comparatively strong, and an elevated actuation force must be furnished by the magnet whereby the directional control seat valve is taken into an open position.
In order to improve the sealing property, the valve seat is pre-pressed. Such pre-pressing is described, e.g., in DE 195 09 145 A1. During pre-pressing the valve seat diameter is reduced in accordance with the pressing width, so that the valve seat then has an accordingly smaller diameter—correspondingly the original valve seat diameter (prior to pressing) must be selected somewhat greater.
If, now, the valve seat is pre-pressed in the solution known from G 91 09 976, the external diameter of the compensating piston must be selected to be correspondingly smaller than the pre-pressed valve seat diameter. If a higher pressure is present at the one port that is connected via the compensating bore with the pressure chamber delimited by the end face of the compensating piston, a force effective in the closing direction acts on the piston owing to this differential area, whereas owing to the differential area the piston is acted on in the opening direction when the other port is subjected to pressure. Correspondingly the spring biasing the closure cone in the closing direction must be designed to be stronger in order to compensate for this differential area. The electromagnet must be designed so as to be able to shift the piston in the opening direction against the pressure forces and the comparatively high spring force.